Graduate School of Natural and Applied Sciences
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Item SITUATIONAL METHOD ENGINEERING FOR REQUIREMENT ENGINEERING PHASE(2009-05-30) AYDIN, Seçil; MISHRA, DeeptiThis thesis focuses on requirements engineering phase and reviews the existing requirement engineering methods and compares them according to the constraints in the software projects. It has been found that some techniques are better suited to particular project teams and circumstances. Besides, methods are normally general in nature and they can not be used directly without adapting them according to the characteristics of the project. This is the concern of situational method engineering, where the term situational method is used to refer to a method tailored to the needs of a particular development setting. A criterion methodology is established to distinguish requirement engineering methods from each other according to different characteristics of the project. A tool is implemented to store different methods according to this criterion methodology by using Situational Method Engineering. This tool is compared with other tools that exist in the literature. The tool is published and validated by collecting data from the industry. The results gathered from the industry are presented and discussed for the improvement of proposed approach.Item NUMERICAL MODELING OF THE AUGUSTUS TEMPLE(2010-01-27) DÖĞER, Rıdvan; SARI, Yasin DursunThis thesis reviews the numerical modeling of the Augustus Temple. “3DEC” software by Itasca and “PLAXIS” software by PLAXIS B.V. were used to perform the numerical analysis. Recommendations for future testing and monitoring were discussed. Analysis methods and properties of dry stone structures were also discussed in this thesis.Item ANALYTICAL INVESTIGATION OF MULTI-LAYER COMPOSITE TUBES SUBJECT TO PRESSURE(2010-01-27) ATLI, Ahmet; AKIŞ, TolgaThe aim of this study is to present an analytical approach for the stress analysis of multi-layer composite tubes under internal and external pressure. The expressions of stresses and displacements for single, two and three-layer tubes are obtained and the critical cases of yielding are examined using Tresca’s and von Mises yield criterion. The analytical solutions are checked numerically for different material sets and the stress and displacement distributions are obtained. It is found that yielding begins at the inner surface of the single layer tubes under internal or external pressure. For the two-layer tubes, yielding may begin at the inner surface of the inner or outer tubes or simultaneously at both locations. For the three layer tubes different cases of yielding may occur depending on the material properties. In the study, the conditions for these various yielding cases are thoroughly examined.Item DESIGN OF TWO WHEELED TWIN ROTORED HYBRID ROBOTIC PLATFORM(2010-07-27) KÜÇÜK, Doğanç; ARIKAN, Kutluk Bilge; İRFANOĞLU, BülentThe design of the two wheeled twin rotored hybrid robot (TWTR) structure is explained in the thesis. This study is the initial phase of the project to reach a hybrid platform that can navigate on ground and hover and navigate in air whenever necessary. This initial phase includes the design of the initial version of the physical system and design of basic controllers depending on the mathematical models and simulations. The system is designed and physically constructed based on the mechatronics design principles. Selection of actuators, sensor set, and the control hardware and the physical structure design are all considered simultaneously with the mathematical model and controller design phases. Nonlinear equations of motion of the physical system are derived and linearized in state space form for both ground and flying modes of motion. Linear Quadratic Regulator (LQR) and Error Space Approach type of controllers are designed employing the mathematical model and simulations. For ground motion, LQR and Error Space Approach controllers are designed and implemented on the real system; whereas PID and LQR type control systems are designed and implemented for the flying motion of the real robotic platform. Stabilization of the attitude dynamics is considered for the flying motion in this study. Designed control systems are implemented on the physical system and the control parameters are tuned experimentally. The control system is developed in Matlab/Simulink and real time implementation is achieved by using Simulink Real Time Windows Target utility. Embedded controllers are not utilized in this first stage. Control systems are designed for the stabilization of the system and error space approach is applied for tracking a reference for the motion of the robot on ground. LQR’s are designed to stabilize the attitude dynamics of the robot for flying motion. Switching between the control systems on ground and in air modes are achieved using a proximity sensor that can sense the distance of the platform body to the ground. Experiments show that system can be stabilized on ground and the attitude dynamics can be stabilized in air. The system will be developed to fully guide on ground and in air.Item INVESTIGATING USE OF UNTENSIONED PRESTRESSING STRANDS IN REINFORCED CONCRETE FLEXURAL MEMBERS(2011-01-26) ARSAVA, Tuğba; BARAN, ErayIn this thesis use of untensioned prestressing strand in flexural members as tension reinforcement is investigated. In manufacturing of prestressed/precast concrete elements prestressing strands are used. According to a questionnaire survey carried out by companies being active in manufacturing of prestressed/precast products it is observed that the remaining pieces of cut strands are used only as lifting hooks. In case these remaining pieces could be used as bending reinforcements, it will be possible to make a more economical use of these high strength products which are imported from abroad. When conventional reinforcing bar and high strength strand compared, high strength strand strands indicate different stress-strain behavior. The fulfillment of the design requirements of the contemporary building regulations about using concrete elements reinforced with high strength strands instead of concrete elements reinforced with conventional reinforcing bars, is still a field which is open to investigation and research. Aiming to contribute closing the gap in literature on the subject issue, a research is carried out consisting of laboratory tests supported by analytical analysis. thirteen reinforced concrete beams prepared, seven out of thirteen beams were reinforced with conventional reinforcing bars and the remaining six beams reinforced with high strength strands. All beams were tested under two point loading. Following the laboratory tests, a numerical parametrical evaluation is carried out on beams with different cross-sectional areas and with different material properties. Following the laboratory tests and the numerical analysis, the behaviour of concrete members which are reinforced with high strength steel strands instead of standard reinforcing bars under bending conditions are evaluated and the differences observed are noted. Finally the applicability of the procedures with regard to provision of moment carrying capacities and the minimum required ductility levels identified in American Concrete Institute (ACI-318) and TS500 regulations to concrete beam elements reinforced with high strength tensile strands are reviewed and summarized.Item A COMBINED EXPERIMENTAL-NUMERICAL INVESTIGATION ON ALUMINIUM EXTRUSION(2011-04-27) KALKAN, Hakan; ÖZDEMİR, İzzet; BARANOĞLU, BesimThis study focuses on an industrial size aluminum extrusion process and consists of both experimental and computational parts. On the basis of process parameters and die geometry supplied by ASAŞ Aluminum Company, full scale computational models of the process have been constructed by using different commercial Finite Element and Finite Volume software packages. The necessary material characterization has been done by compression tests for which a new uni-axial compression test set-up suitable for high temperatures has been designed and manufactured. The measured load-displacement diagrams and exit temperatures are compared with the computational results. In addition to that, Finite Element and Finite Volume results are also compared. These results indicate that reasonable good agreement between the measured data and computational results can be achieved provided that the Finite Element Method is used and proper material characterization is conducted.Item TOWARDS REAL TIME IMPLEMENTATION OF SPECIFIC EMITTER IDENTIFICATION ON PULSE WAVEFORMS: OPTIMIZATIONS ON A LOW COST COMMERCIAL PLATFORM(2012-01-25) ERDEM, Cihangir; KARA, AliSpecific Emitter Identification (SEI) methods are used in intercept systems for differentiating of same type of emitters in the environment. Most of the SEI implementations are designed for post processing (off line) by operators. This thesis presents results of study towards the real time (on line) implementation of a SEI method on signals after the IF stage, i.e. video signals (envelope) after the detector section. Initially, only the envelopes of the pulses are considered in SEI processing. Pulse width, rise time, fall time, rise slope angle, fall slope angle and pulse point are main parameters used in SEI algorithm developed. On the other hand, one of the main problems in operational environments is multipath distortion on received pulses. Moreover, creating and running of a library is another important issue. This thesis presents various approaches in both processing of multipath distorted pulses and wavelet based library creation methods on real-time SEI implementation for an intercept receiver.Item A METHODOLOGICAL APPROACH FOR SERIOUS GAME SOFTWARE DEVELOPMENT: AN APPLICATION FOR LANGUAGE DISORDERS(2012-01-25) ÇAĞATAY, Mehmet; EGE, Pınar; ÇAĞILTAY, NergizThe computer software has been actively used in education area in different ways today. However, for several reasons educational institutions are failing to integrate this software to current educational environments. Educational institutions have been criticized for using technologies similar to the ones used hundred years ago. We believe that, one of the reasons for this failure, integration of educational software technologies into current educational environments, is the complexity of these systems. Hence developing efficient software by addressing the real life problems is a complex process. There are various software development methodologies especially for complex software, with regular and planned development processes. So far, these software development methodologies are appropriate for almost all software, though, in terms of unique needs and developmental process of educational software, they may be inadequate. In other words, development of the educational software process requires some other considerations, such as the domain experts that are not considered during the development process of commercial software projects. In this thesis, a new educational software development methodology by involving the domain experts and their interactions with the end users is recommended. Additionally, this software development methodology is used in a serious game development process that supports the therapy process of children with impaired speech and language. Primarily in this study, the contribution of the serious game on the current therapy sessions is evaluated which is developed by using the proposed educational software development methodology. It is aimed to better address the problems of current therapy sessions by developing the software according to the new methodological approach. In other words, this study is a case study to show how the proposed methodology is applied on the development process of a serious game as well as its impact on current therapy sessions.Item THERMOELASTIC ANALYSIS OF HEAT GENERATING MULTI-LAYERED COMPOSITE CYLINDERS AND TUBES(2012-04-18) YILDIRIM, Murat; ARGEŞO, HakanA computational method is developed for the thermoelastic analysis of internally heat generating multi-layered composite cylinders and tubes having temperature dependent physical properties. The composite assembly is considered to be infinitely long and have axially constrained ends. In the formulations, small deformation theory is used. The layers that form the composite assembly are isotropic and have uniform heat generation. The thermal and mechanical problems are uncoupled and axisymmetric. The thermal problem is steady state and the mechanical problem is a plane strain problem. The computational model is based shooting algorithm. Both the thermal and mechanical problems are solved with the use of shooting algorithm. The computational model is first verified through the use of some benchmark problems that have analytical solutions in which the physical properties are considered to be temperature independent. The computational method is then used to solve some composite cylinder/tube assemblies that have temperature dependent physical properties.Item EFFECT OF AUSTEMPERING ON THE MICROSTRUCTURAL AND BALLISTIC PROPERTIES OF MIL-A-12560 AND AISI 4340 STEELS(2012-10-25) DEMİRCİ, Ali Tunç; TEKİN, ErdoğanThis thesis is prepared in order to show the possibilites of the development of bainitic steel armor plates from U.S. Military Standard, MIL-A-12560 and alternatively, AISI 4340 steel to protect the civillian and military vehicles against external threats.Item TOWARDS REAL TIME IMPLEMENTATION OF SPECIFIC EMITTER IDENTIFICATION ON PULSE WAVEFORMS: OPTIMIZATIONS ON A LOW COST COMMERCIAL PLATFORM(2012-10-29) ERDEM, Cihangir; KARA, AliSpecific Emitter Identification (SEI) methods are used in intercept systems for differentiating of same type of emitters in the environment. Most of the SEI implementations are designed for post processing (off line) by operators. This thesis presents results of study towards the real time (on line) implementation of a SEI method on signals after the IF stage, i.e. video signals (envelope) after the detector section. Initially, only the envelopes of the pulses are considered in SEI processing. Pulse width, rise time, fall time, rise slope angle, fall slope angle and pulse point are main parameters used in SEI algorithm developed. On the other hand, one of the main problems in operational environments is multipath distortion on received pulses. Moreover, creating and running of a library is another important issue. This thesis presents various approaches in both processing of multipath distorted pulses and wavelet based library creation methods on real-time SEI implementation for an intercept receiver.Item DESIGN OF A MODULAR EDUCATIONAL SET-UP FOR MECHATRONICS ENGINEERING(2013-03-22) AYHAN, Emre; ERDEN, ZühalThis thesis is a study on modular mechatronic product design. The main purpose of this study is to implement heuristic approach to the modular design of a mechatronic product family. The heuristic method has been developed and applied for the design of mechanical product families. Thus, main contribution of this thesis is the application of the method in the mechatronic design field. In this study, the selected product family is an educational mechatronic set-up which will be used for the sophomore mechatronics design course in the Mechatronics Engineering Department of Atılım University. This research includes implementation of the heuristic design methodology and conceptual design for the mechatronics educational set-up, as well as its physical design and manufacturing.Item PERFORMANCE BENCHMARKING OF CELLULAR NETWORK OPERATORS IN TURKEY(2013-04-22) KADIOĞLU, Rana; KARA, AliThis thesis is prepared for assessing and benchmarking network operators‘ service quality on the basis of QoS. In order to make comparisons between mobile operators‘ service quality, appropriate performance indicators are identified. Performance is evaluated by key performance indicators. Performance indicators are obtained by vehicle test method on a specified route for each operator to be compared. One of the most important indicators, voice quality benchmarking is performed by χ² and Fisher test. These statistical methods for benchmarking are explained and results are discussed.Item EXPERIMENTAL INVESTIGATION OF INFLUENCE PARAMETERS ON FORMING LIMIT DIAGRAMS OF ALUMINUM ALLOY-AL 2024(2013-04-22) ÇELİK, Gökhan; KAFTANOĞLU, Bilgin; KARADOĞAN, CelalettinSheet metal forming is the key word for aerospace, automobile and aeronautics industry. To fulfill the customer expectations, safety requirements and market competitions, sheet metal forming processes must be well analyzed before production. At this stage, importance of material characterization and finite element (FE) simulations arise. This study is focused on combination of material characterization and FEA (Finite Element Analyses) of sheet metals to be able to make improvements of sheet metal while considering cost and quality. On the material characterization parts of the study, simple tension tests, hydraulic bulge tests (HBT) and forming limit diagrams are determined for Al2024 aluminum alloy. HBT is obtained using a new specialized code and compared to the simple tension tests. High accuracy mechanical extensometers are used to obtain instantaneous deformation during tensile test and similarly high accuracy CCD cameras are used to obtain material deformation during determination of FLDs and flow curves from HBT. FE studies are performed to validate experimental studies and to determine coefficient of frictions of different lubricants. Analyses are carried out using a commercial FE package, Marc Mentat 2007® . Material inputs are supplied from experimental uniaxial and hydraulic bulge tests. Flow curve validations are performed comparing HBT and uniaxial tensile tests up to 0.15 strains. Experiments revealed that initial material thickness and lubrication has a significant effect on formability window of aluminum sheets and speed of punch has no great effect on limits of aluminum formability since Al2024 is a strain rate independent material. Beside these, higher strains than uniaxial tensile test are obtained in HBT with new developed code.Item ATTITUDE AND ALTITUDE CONTROL OF TWO WHEEL TRIROTOR HYBRID ROBOT(2013-05-21) ALWAFI, Husein; İRFANOĞLU, Bülent; ARIKAN, Kutluk BilgeTwo Wheel Tri-Rotor (2W3R) hybrid robot that can move on ground, hover and navigate in air, is a novel system studied in this thesis. Physical structure of the system had been built in Flying Robotics Laboratory by undergraduate students as a course project in Mechatronics Department at Atılım University. Core of this thesis is to design controllers to stabilize and control the system on its hovering conditions. Stabilization and control of roll, yaw, pitch, and the altitude dynamics using the propulsion units are studied. Nonlinear equations of motion of the physical system are first derived, and then state feedback linearization technique and Linear Quadratic Regulator (LQR) are used, and control systems are developed in Matlab Simulink.Item A BIOINSPIRED CONCEPTUAL DESIGN METHODOLOGY FOR BIOROBOTS(2013-05-21) KONEZ EROĞLU, Aylin; ERDEN, Abdülkadir; ERDEN, ZühalThe main aim of this thesis is to develop a Bioinspired Conceptual Design (BICD) methodology for design of biorobots. Within the context of the dissertation, a novel BICD procedure has been developed based on existing BID approaches and systematic engineering design steps. This procedure is applied on several case studies, namely a dog biorobot (BioDog) for walking and trotting, a cockroach biorobot (BioCoc) for climbing, a jumping (grasshopper) biorobot for jumping and a hybrid (dog and lobster) biorobot for walking. A BICD process has been developed using the implementation results. Classic DEVS (Discrete Event System Specification) coupled model is used to formally represent the BICD process in order to develop a BICD methodology. The proposed BICD methodology transforms customer needs into a concept design of biorobot with clear and well-defined six design steps. In order to overcome the drawbacks of existing BIDs, the biological system analysis and the bioinspired transformation design steps have been considered in detail. In this thesis, although four case studies have been implemented to demonstrate the BICD methodology, fourteen biological systems and twenty four locomotion types are investigated by using content analysis and/or observation methods. The literature survey has been used for the content analysis method, while an experimental set-up is used to analyze the biological systems for the observation method. Required knowledge on morphology, function and behavior of biological systems are obtained using a high speed camera. During the bioinspired transformation step, the knowledge about the biological system has been transformed systematically into knowledge about the biorobots and this knowledge is used to develop the concept design of biorobots.Item ASSESSMENT OF INTELLECTUAL CAPITAL BY USING NEW FUZZY ANALYTIC NETWORK PROCESS APPROACH(2013-06-14) ÖZDEMİR, Yavuz Selim; ERKAN, Turan ErmanThe value of an enterprise is made of financial assets and intangible assets which called as Intellectual Capital. Intellectual Capital has always existed, but only in the last decades awareness of its strategic importance has increased becuase of the shift in modern economy from the industrial to the knowledge era. Both academics and experts in the business world agree that Intellectual Capital is one of the most important points to maintain competitive advantage in today's markets. Intellectual Capital consists of non-physical sources of value related to Human Capital and Structural Capital. IN the scope of this thesis, a new Fuzzy Analytic Network Process approach was proposed for evaluation of the relative importance of Intellectual Capital components and it has been investigated in terms of satisfaction indicators of Intellectual Capital. This proposed new methodolgy compared with other most commonly used Fuzzy Analytic Network Process methodologies in the literature. A group of experts has been chosen for IC criteria evaluation. The obtained results used for evaluation of sectorial awareness levels for manufacturing and service sectors in Ankara area.Item A COMBINED NUMERICAL-EXPERIMENTAL INVESTIGATION ON MICRO-EXTRUSION(2013-06-14) MURAT, Levent; ÖZDEMİR, İzzet; ŞENGÖNÜL, MerihIn this work, to develop an understanding on micro forming processes, a combined experimental-numerical investigation on micro forming is presented. On the experi mental side, in order to demonstrate the statistical size effect, an experimental set-up for micro-extrusion has been designed and micro-extrusion test with copper billets of different average grain size, has been conducted successfully. On the modelling side, due to large displacement and large strains developing during the forming process, a geometrically non-linear continuum mechanics description is preferred. Since a grain level description is necessary for micro forming operations, crystal plasticity is used to model the mechanical response of each grain. To this end, the crystal plasticity framework has been coded as a user defined material model and integrated into the commercial FE software Abaqus as a UMAT subroutine. With this tool, a numerical investigation on the influence of grain orientations on frictional response at small scales is carried out.Item LATERAL LOAD BEHAVIOR OF COLD-FORMED STEEL WALL PANELS(2013-06-15) ALICA, Hüseyin Çağatay; BARAN, ErayIn this thesis, lateral load behavior of cold-formed steel (CFS) wall panels was investigated. For this purpose full-scale CFS wall panel specimens were tested experimentally. Measured load capacity of wall panels were also compared with numerically predicted values. Experimental part of the study included monotonic lateral load testing of twenty one CFS wall panels. Wall panels were sheathed with oriented strand board (OSB), fibercement and betopan panels. Influence of additional parameters, such as sheathing panel thickness, screw spacing, CFS section size, existence of diagonal struts and double-sided sheathing was also investigated. Using the information obtained from load tests, the lateral behavior of the wall panels was studied and the differences and similarities in the response of these panels were investigated. Response of wall panels under lateral loading was determined to be directly related with the behavior of the hold-down attachment used at the base of panels. In most of the specimens tested in this study, the strength and stiffness of the hold-down attachment prevented the wall panels to reach the expected strength and stiffness levels. Among the parameters investigated in this study the one that had the most significant effect on the behavior of wall panels was the screw spacing used at exterior framing members. Between the cases of 15 cm and 30 cm screw spacing, the increase in load capacity of wall panels was between 37% and 85% depending on the type and thickness of sheathing panel.Item EXPERIMENTAL AND NUMERICAL STUDY ON STRETCH FORMING PROCESS(2013-06-20) ALKAŞ, Celal Onur; KARADOĞAN, Celalettin; ŞİMŞİR, CanerStretch forming process is commonly used in the aircraft industry for the manufacturing of large sheet panels. The success of this process is highly dependent on the process parameters like mechanical properties of sheet material, the friction condition between tools-part interfaces and relative motions between tool and jaws. Determining the best parameters by trial - error procedure is quite difficult and costly, so that finite element analysis is needed. The scope of this study is to establish finite element model (FEM) for stretch forming process. For this purpose, accurate material and reliable friction modeling are required. Material characterization tests of mostly used aluminum alloys are conducted to prepare input to the model. Standard tensile, stack compression, hydraulic bulge test (HBT) and forming limit diagram (FLD) tests are performed in order to identify deformation behavior and anisotropy properties of aluminum sheet materials. High accuracy CCD cameras are used to obtain material deformation during determination of FLDs and flow curves from HBT. Also, friction coefficients are determined for various lubrication conditions encountered in stretch forming processes using inverse based analysis. Using these inputs, numerical model of the process is established by FEM for three basic stretching tool motions, which are; stretching the sheet by jaw, stretching the sheet by form die and finally stretching the sheet material by synchronized motion of both tools. In order to improve the model and validate the analyses results, experimental work is also performed in which the deformation of the sheet is measured optically using GOM-Argus® 3- D deformation measurement device. Then, three selected aerospace sheet parts were analyzed and success of the model for industrial applications is proved.